XRD diffraction pattern of bimetallic Pt/Ru nanoclusters [13].Table 2. Effect of water content in EG on the particfe size of Pt nanoparticles deposited on MWNTs

Source:. Refs. [20,21] first step of the synthesis process. Therefore, the particle size and the size distribution of the unprotected metal nanoclusters can be controlled to some extent by simply

adjusting the content of water in the starting reaction mixture. A great advantage of the solvent and simple ionstabilized metal nanoclusters prepared according to the alkaline EG synthesis method is that they can be conveniently separated as precipitates from the original colloidal

solution by adding a dilute aqueous solution of HCl, adjusting the colloidal solution to be acidic. Based on different requirements in application, the precipitated metal

nanoclusters can be redispersed into many kinds of organic solvents, such as alcohol, ketone, THF, acetonitrile, DMF and DMSO, giving rise to different colloidal solutions of the unprotected metal nanoclusters. It was found that the Pt nanoclusters "dissolved" in some ketone solvents as well as DMF and DMSO were very stable. For example, the colloidal solution of Pt nanoclusters in cyclohexanone or cyclopentanone was transparent and homogeneous, no precipitate was observed after standing for at least several months. Besides, the metal concentration of Pt nanoclusters in colloidal solutions

could be elevated to a level higher than 200g/l by this separation redispersion procedure. TEM characterizations showed that the Pt nanoclusters in these colloidal

solutions had an average diameter of l-2 nm, indicating that no obvious aggregation of the small Pt particles occurred during the transferring process. Based on a series of experimental phenomena, it was suggested that EG adopted in the alkaline EG synthesis y Wang and XWang method acts not only as a solvent and a reductant, but also as a stabilizer [11]. When other glycols such as l,2propylene-glycol and l,4-butylene-glycol were used in the

similar reaction conditions, it was hard to prepare stable metal colloidal solutions of unprotected metal nanoclusters as reported by Liu and co-workers In the alkaline EG synthesis method, the pH value of the reaction mixture is very important for producing stable metal nanoparticles in EG. If the pH value is not high enough, instead of a metal colloidal solution, a metal precipitate will be obtained in the subsequent reduction process under heating [11]. During the reaction process, NaOH would react with metal chlorides and some organic acid resulted from the oxidation of EG; therefore, pH of